Fig. 7

Roof-plate dependent regulation of rhombomere boundary signals. (A–H) wnt1 expression in controls (A, B and E, F) and Lmx1b double morphants (C, D and G, H) at 18 hpf (A, B) and 24 hpf (E, F), dorsal view (A, C and E, G) and lateral view (B, D and F, H). The wnt1 expression pattern is not changed in Lmx1b morphants at 18 hpf compared to controls (A–D), whereas in 24 hpf Lmx1b morphants, wnt1 expression is specifically down-regulated in rhombomere boundaries (F, H) compared to 24 hpf controls (E, G). Notice the uniform expression of wnt1 in the dorsal hindbrain of Lmx morphants (G, H), indicating that elevated levels of wnt1 in rhombomere boundaries are not maintained in the absence of lmx1b-dependent roof plate development. Asterisks in panels C, D, G, H denote loss of wnt1 expression in MHB (midbrain–hindbrain boundary) of Lmx1b morphants. (I–T) lmx1b.2 expression in controls (I, J, O, P), Wnt1 morphants (K, L, Q, R), and Rfng morphants (M, N, S, T) at 18 hpf (I–N) and 24 hpf (O–T), dorsal view (I, K, M, O, Q, S) and lateral view (J, L, N, P, R, T). In control embryos, dorsal hindbrain lmx1b.2expression is restricted to the roof plate cells (I, J, O, P), while in Wnt1 morphants, lmx1b.2 expression is expanded throughout the dorsal hindbrain (K, L, Q, R), indicating that dorsal hindbrain Wnt1 signals are required for the restriction of lmx1b.2 expression to the roof plate. By contrast, in Rfng morphants, in which wnt1 signals are down-regulated exclusively in rhombomere boundaries (M, N, S, T), lmx1b.2 expression is not altered compared to controls (I, J, O, P), indicating that rhombomere boundary-derived signals do not control the expression of lmx1b.2 expression in the dorsal hindbrain.